This seems to be a Performance Power 850W 533mm Belt Sander PBS850A from B&Q.
One takes it that you have done the obvious and tried a Gooogle search for "performance power tool spares" or similar. Weren't Solent Tools any use?
https://www.solenttools.co.uk/p0/performance-power/314604.htm
Its a problem with all the pile it high and sell cheap stuff that spares and support are minimal. Its one of the things you pay for in a main brand.
wettqr, November 2017
